1. Field of the Invention
This invention relates to an ignition control device for a low tension distribution system in an internal combustion engine.
2. Discussion of Background
Conventional ignition timing control devices are of two types: one is a high tension distribution system, in which a high tension voltage is applied to the ingnition plug for each engine cylinder through a single rotor; and the other is a low tension distribution system, in which a drive signal is distributed to each ignition plug provided in each engine cylinder. This low tension distribution system is used for the purpose of improving the engine performance by increasing the ignition energy, reducing the sources of noise by elimination of high tension power distribution, improving quality of the device as the commercial product to be circulated in the market, and so on.
FIG. 1 of the accompanying drawing shows the ignition timing control device in the low tension distribution system, in which a reference numeral 1 designates a four-cylinder engine; a numeral 2 refers to an ignition plug provided in each of the engine cylinders; a reference numeral 3 denotes a throttle valve provided in an air intake pipe 4; a reference numeral 5 represents a Karman's vortex type air flow sensor (hereinafter abbreviated as "AFS") which is disposed at the inlet port of the air intake pipe 4 and for detecting a quantity of intake air; a numeral 6 refers to an air cleaner which is provided at a further inlet side of the AFS 5; a reference numeral 7 denotes a crank shaft angle sensor for detecting revolution of the engine 1, which generates a crank angle reference signal (SGT) and a cylinder discrimination signal (SGC); a numeral 8 refers to a first ignition coil for imparting a high tension voltage to the first and fourth ignition plugs 2; a reference numeral 9 denotes a second ignition coil for imparting a high tension voltage to the second and third ignition plugs 2; a reference numeral 10 designates an ignition control section; numerals 11 to 13 represent interfaces; numerals 14 and 15 refer respectively to first and second counters; numerals 16 to 18 respectively refer to first to third timers; a numeral 19 refers to a CPU (central processing unit) having ROM and RAM; numerals 20 and 21 designate AND circuits; 22 and 23 refer to drivers; 24 refers to an A/D converter; and 25 and 26 refer to transistors.
In the above-described construction, SGT, SGC and an output from the AFS 5 are introduced as inputs into the ignition control section 10, from which a drive signal is forwarded to the ignition coils 8 and 9 alternately through the drivers 23 and 22, respectively, to bring about spark on the first and fourth ignition plugs 2 and the second and third ignition plugs 2, alternately, whereby the first to fourth cylinders are ignited in sequence (note should be taken that, when one of the cylinders is in its compression stroke, the other cylinder is in its exhaust stroke, hence there is no possibility of the two cylinders being ignited simultaneously).
With the above-described conventional device, however, since distribution of the drive signal to each of the ignition coils 8 and 9 is dependent on SGC, if there takes place an abnormal situation in the SGC due to insufficient contact in the connectors, wiring breakage in the harness of the car body, malfunction in the crank angle sensor 7, and so forth, regular distribution of the drive signals cannot be warranted with the consequent inability of the engine to run, destruction of the engine 1 due to erroneous ignition, and others.
FIG. 2(A) indicates various operating waveforms at different sections in the ignition timing control device when the SGC is normal, wherein (a) indicates the waveform of SGC; (b) indicates that of SGT; (c) shows that of an output signal from the third timer 18; (d) denotes an output signal from a port P6 of the CPU 19, this output being at its high level (H), when SGC is at its high level (H) at the time of rising of the SGT, and being at its low level (L) when SGC is at its low level (L) at the time of rising of the SGT; (e) denotes that of an output from the port P7, which is at its low level (L) when the output from the port P6 is at its high level (H), and is at its high level (L) when the output from the port P6 is at its low level (L); (f) indicates that of a drive signal for the ignition coil 8 for the first and fourth ignition plugs 2, which signal is obtained from outputs of the timer 18 and the port P6 introduced as inputs into the AND circuit 21, from which an output as the drive signal is forwarded to the ignition coils through the driver 23; and (g) designates that of a drive signal for the ignition coil 9 for the second and third ignition plugs 2, the signal being obtained by alternately forwarding an output from the timer 18 into the AND circuits 20 and 21, during which either of the ignition coils 8, 9 the becomes electrically conducted, and, at the time of shutting the electric current conduction, spark is generated in any of the ignition plugs 2, thereby carrying out sequential ignition of each and every cylinder.
FIG. 2(B) indicates various operating waveforms at different sections in the ignition timing control device when SGC stops. In the drawing, (a) indicates the waveform of the SGC, in which those waveform portions represented by dotted lines are lacking; (b) shows that of the SGT, which is the same waveform as that when the SGT is normal; (c) shows that of the output from the timer 18 which is also normal; (d) and (e) denote various waveforms of the outputs from the ports P6 and P7 respectively; and (f) and (g) denote waveforms of the drive signals for the ignition coils 8 and 9, respectively, in which the drive signal (g) contains therein erroneous distribution portions as indicated by diagonal hatch lines, which are liable to cause inability of the engine to run or destruction of the engine due to erroneous ignition.
Further, there occur various noises in the engine 1, and these noises, when superposed on the SGC, become unable to be eliminated, depending on its magnitude, even with a filter circuit. On accont of this superposition of the noises on the SGC, there take place problems such that, due to erroneous reading of the SGC, the drive signals for the ignition coils 8 and 9 cannot be regularly distributed to thereby cause inability of the engine to run or destruction of the same due to erroneous ignition, or others.